According to the related art, a radar apparatus of a vehicle outputs a transmission wave from the antenna of the radar apparatus. If the output transmission wave is reflected from a target and the reflected wave is received by the antenna, the radar apparatus derives the position of the target relative to the vehicle (the radar apparatus). The detailed process is as follows. In the radar apparatus, a signal processing unit mixes a transmission signal which corresponds to the transmission wave and whose frequency varies with a predetermined period, and a reception signal which corresponds to the reflected wave, thereby generating a beat signal. Specifically, the predetermined period of the transmission signal includes an UP section where the frequency increases and a DOWN section where the frequency decreases, and the signal processing unit generates a signal (hereinafter, referred to as a “beat signal”) based on the frequency difference between the reception signal and the transmission signal (which is a beat frequency) in each of the UP section and the DOWN section.
Next, the signal processing unit takes the Fast Fourier Transform (FFT) of each beat signal, thereby generating signals of different frequencies (hereinafter, referred to as “transformed signals”), and detects signals exceeding a predetermined signal level threshold as peak signals from the transformed signals. Then, on the basis of information such as the signal levels and frequencies of the peak signals, the signal processing unit pairs a peak signal of the UP section corresponding to one target, and a peak signal of the DOWN section corresponding to the same target, thereby deriving pair data.
Next, on the basis of the pair data, the signal processing unit derives a distance until the reflected wave reflected from the target arrives a receiving antenna 14 of a radar apparatus 1 (hereinafter, referred to as a “longitudinal distance”). Also, the signal processing unit derives the distance between the vehicle and the target in a lateral direction relative to the traveling direction of the vehicle (hereinafter, referred to as a “lateral distance”). In other words, on the basis of the pair data, the signal processing unit derives information on the position of the target as seen from the vehicle. Further, the signal processing unit derives a relative speed which is the speed of the target relative to the running vehicle. As target categories based on relative speeds, for example, there are stationary targets having almost the same relative speed as the speed of the vehicle and moving targets having relative speeds different from the speed of the vehicle. Next, the radar apparatus outputs the derived information such as the position of a moving target to a vehicle control unit for controlling the operation of the vehicle. As a result, the vehicle control unit performs necessary control on the vehicle according to the position of the moving target and the like output from the radar apparatus. Also, as a reference for explaining a technology related to the present invention, there is Patent Document 1.
Patent Document 1: Japanese Patent Application Publication No. 2009-133761
However, for example, in a case where the vehicle is traveling at a place where stationary targets are derived in relatively large numbers, like in a tunnel, the signal processing unit of the radar apparatus cannot derive information such as the origin positions of the targets. In other words, in a frequency band where there are a number of peak signals corresponding to a continuing stationary target like in a tunnel, pairing of peak signals (hereinafter, referred to as “movement peak signals”) corresponding to a moving target may not be appropriately performed. Specifically, without paring the movement peak signal of the UP section and the movement peak signal of the DOWN section, the movement peak signal of the UP section and a stationary peak signal of the DOWN section may be paired, or a stationary peak signal of the UP section and the movement peak signal of the DOWN section may be paired. As a result, pair data based on the movement peak signals may not be derived and thus information such as the position of the moving target may not be derived.
Also, in a case where the signal level of a stationary peak signal existing in the vicinity of the frequency of a movement peak signal is higher than the signal level of the movement peak signal, the movement peak signal may be included in the stationary peak signal, and thus pairing of the movement peak signal of the UP section and the movement peak signal of the DOWN section may not be performed. As a result, pair data based on the movement peak signals may not be derived and thus information such as the position of the moving target may not be derived. As a result, sometimes the vehicle control unit cannot perform necessary control on the vehicle on the basis of information such as the position of the moving target output from the radar apparatus.